Paper feed roller and image forming apparatus with the paper feed roller

ABSTRACT

The invention provides a paper feed roller capable of reducing abnormal noise caused by a knurled shape while maintaining characteristics thereof, including maintaining friction coefficient and coping with paper powder. The paper feed roller comprises a roller body formed of elastic material in a cylindrical shape and is characterized in that the roller body has protruding lines and recessed grooves inclinedly extending relative to an axis of the roller body so that convex and concave portions having predetermined widths are alternatively formed in a circumferential direction of a peripheral surface, and the protruding lines have one-end side protruding line portions extending from a central part in an axial direction of the roller body toward one end thereof and other-end side protruding line portions extending from the central part in the axial direction toward the other end, and they are inclined relative to the axis in opposite directions.

TECHNICAL FIELD

The present invention relates to a paper feed roller and image forming apparatus with the paper feed roller.

BACKGROUND OF THE INVENTION

Various kinds of paper feed rollers are incorporated in paper feeding mechanisms in order to carry paper. A paper feed roller is generally formed of elastic material such as crosslinked rubber in a cylindrical shape and comprises a roller body whose peripheral surface is a contact surface to paper. Also, in the recent years, a paper feed roller (see, for example, JP 2015-178392 A) having concave and convex shapes arranged in a circumferential direction at even intervals (hereinafter, a knurled shape) is widely used to maintain satisfactory friction coefficient in the long term and to cope with paper powder from poor quality paper.

SUMMARY OF THE INVENTION

However, the paper feed roller having the knurled shape on its peripheral surface causes abnormal noise which does not occur to a round tubular paper feed roller by rotating the paper feed roller at high speed. It is considered to be because when an outer surface of a paper feed roller is in the knurled shape, rubber of the peripheral surface of the paper feed roller and paper repeat contacting and separating during paper passing.

The present invention has been made in the light of the problems mentioned above, and the object of the present invention is to provide a paper feed roller which is able to reduce abnormal noise caused by a knurled shape while maintaining characteristics of the knurled shape, such as maintaining friction coefficient and coping with paper powder.

A paper feed roller of the present invention comprises a roller body formed of elastic material in a cylindrical shape, and the paper feed roller is characterized in that the roller body includes a plurality of protruding lines and recessed grooves inclinedly extending relative to an axis of the roller body so that convex portions with predetermined width and concave portions with predetermined width are alternatively formed in a circumferential direction of a peripheral surface of the roller body, and the plurality of protruding lines include one-end side protruding line portions extending from a central part of the roller body in a direction of an axis of the roller body toward one end of the roller body and other-end side protruding line portions extending from the central part in the direction of the axis of the roller body toward an other end of the roller body, and the one-end side protruding line portions and the other-end side protruding line portions are inclined relative to the axis of the roller body in opposite directions each other.

Also, it is preferable that the one-end side protruding line portions and the other-end side protruding line portions extend at substantially equal angles relative to the axis of the roller body and the angles of extending directions of the one-end side protruding line portions and the other-end side protruding line portions relative to the axis of the roller body are no less than 5° or more and 15° or less relative to the axis of the roller body.

Also, it is preferable that the one-end side protruding line portions and the other-end side protruding line portions are provided so that ends of the one-end side protruding line portions at the central part of the roller body and ends of the other-end side protruding line portions at the central part of the roller body are offset in the circumferential direction of the roller body.

Also, the image forming apparatus of the present invention is characterized by comprising the above paper feed roller.

The paper feed roller and image forming apparatus of the present invention is able to maintain friction coefficient and to cope with paper powder, as well as to reduce abnormal noise caused by the shape of the paper feed roller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically illustrated perspective view depicting an entire shape of a paper feed roller of one embodiment of the present invention.

FIG. 2 is a sectional view near a peripheral surface of a roller body sectioned in an orthogonal direction to a direction of an axis of the roller body, depicting convex portions and concave portions of the paper feed roller of FIG. 1.

FIG. 3 is a schematically illustrated side view depicting protruding lines and recessed grooves formed on a paper feed roller of one embodiment of the present invention.

FIG. 4 is a schematically illustrated side view depicting protruding lines and recessed grooves formed on a paper feed roller of other embodiment.

FIG. 5 is a schematically illustrated side view depicting protruding lines and recessed grooves formed on a paper feed roller of another embodiment.

DETAILED DESCRIPTION

A paper feed roller of one aspect of the present invention will be described in the following with reference to figures. It should be noted that a paper feed roller of the present invention can be used as various kinds of paper feed rollers such as a paper feeding roller, a carrier roller, a platen roller, and a paper ejecting roller which are incorporated in paper feeding mechanisms of, for example, an electrostatic copying machine, a laser printer, a normal paper facsimile apparatus, and a multifunction machine of those, or an image forming apparatus such as an inkjet printer, as well as machines such as an automated teller machine (ATM).

As shown in FIG. 1, a paper feed roller 1 of this embodiment comprises a substantially cylindrical roller body 2 integrally formed of elastic material and a shaft 4 inserted through a through hole 3 in the center of the roller body 2. It should be noted that in FIG. 1 protruding lines and recessed grooves formed on a peripheral surface 5 of the roller body 2, which will be described later, are omitted. The shaft 4 is formed, for example, of metal, ceramic, hard resin, and etc. The paper feed roller 1 is mounted to an image forming apparatus, which is not shown, and the shaft 4 is driven by a drive section such as a motor so that the paper feed roller is rotated. The roller body 2 feeds paper by contacting the paper fed to the roller body 2. In this embodiment, as shown in FIGS. 2 to 5, the roller body 2 includes a plurality of protruding lines 21 and recessed grooves 22 which extend inclinedly relative to an axis X of the roller body 2 so that convex portions CV with predetermined width and concave portions CC with predetermined width are alternatively formed in a circumferential direction of a peripheral surface 5 of the roller body 2. It should be noted that in FIGS. 3 to 5 dots are added to portions of the recessed grooves so that the protruding lines 21 and the recessed grooves 22 are easy to see. The protruding lines 21 and the recessed grooves 22 will be described later.

It is preferable that the roller body 2 is formed of elastic material such as rubber and integrally formed, for example, with a crosslinked product of a rubber composition which include ethylene-propylene rubber as a rubber content and peroxide as a crosslinking agent. A crosslinked product of a rubber composition has excellent low-temperature characteristics, and, for example, even under a low temperature and low humidity environment it ensures sufficient flexibility, allowing the roller body 2 to maintain its contact pressure to paper as well as a good coefficient of friction. Thus, the effectiveness of preventing defective paper carrying can be improved by maintaining a good coefficient of friction, especially when used under a low temperature and low humidity environment, for a long time from the early period of use.

It is preferable that a rubber content which becomes a base of the rubber composition includes ethylene-propylene rubber and IR (isoprene rubber) and also the mass ratio of IR to ethylene-propylene rubber is equal to or more than 90/10 and is equal to or less than 50/50. IR has a lower affinity than ethylene-propylene rubber to an organic component such as a sizing agent, which is included in paper powder and acts to adhere the paper powder to a surface of a roller body. Therefore, the adhesion of paper powder to the peripheral surface of the roller body 2 can be inhibited more effectively by blending IR in the above ratio. Also, because IR has a low glass transition temperature, the low-temperature characteristics of the crosslinked products can be further improved by blending IR in the above ratio. Therefore, a good coefficient of friction is maintained and the effectiveness of preventing defective paper carrying can be further improved for a long time from the early period of use even when the roller is used with paper including especially high content of ash content or even when used under a low temperature and low humidity environment.

As examples of ethylene-propylene rubber, ethylene-propylene rubber (EPM) in a narrow sense which is a copolymer of ethylene and propylene and ethylene-propylene diene rubber (EPDM), which is a copolymer of ethylene, propylene, and diene, are included, and EPDM is especially preferable. As EPDM, any of various copolymers in which ethylene, propylene, and diene are copolymerized can be used. As examples of diene, ethylidene norbornane (ENB) and dicyclopentadiene (DCPD) are included. Also, as EPDM, either a so-called oil-extended EPDM, which is extended with extender oil, or non-oil-extended EPDM, which is not extended with extender oil, may be used. However, oil-extended EPDM is preferable for EPDM in consideration of improving processability and so on in preparing a rubber composition by blending an addition agent such as a crosslinking agent into two kinds of rubber contents and kneading them and in forming the rubber composition into a shape of paper feed roller.

Examples of ENB-based oil-extended EPDM, in which ENB is diene, include one or more of those such as ESPLENE™ 670F (rubber content to extender oil=100:100 (mass ratio)) and 671F (rubber content to extender oil=100:70 (mass ratio)) manufactured by Sumitomo Chemical Co., Ltd. and Mitsui EPT3042E (rubber content to extender oil=100:120 (mass ratio)) manufactured by Mitsui Chemicals. Examples of DCPD-based oil-extended EPDM, in which DCPD is diene, include ESPLENE 400 (rubber content to extender oil=100:100 (mass ratio)) manufactured by Sumitomo Chemical Co., Ltd. and so on. Any one of the examples of EPDM mentioned above can be used alone or two or more of those can be used together.

When oil-extended EPDM is used as EPDM, the ratio of IR described above is the ratio to the rubber content (EPDM) included in the oil-extended EPDM. As IR, any of various kinds of IR such as ones whose isoprene is synthesized by a solution polymerization method using Ziegler catalyst, lithium catalyst, and so on can be used. Examples of IR include, but are not limited to, at least one of those such as NIPOL® IR2200 (specific gravity: 0.91, Mooney viscosity (central value): 82), IR2200L (specific gravity: 0.91, Mooney viscosity (central value): 70) manufactured by Nippon Zeon Co., Ltd.

A peroxide crosslinking agent, unlike conventional sulfur-crosslinking-based crosslinking agents, does not need to be used with a vulcanization accelerator or a vulcanization accelerator aid (such as stearic acid), which blooms on a peripheral surface 5 of a roller body 2 and so on and decrease the coefficient of friction and, in addition, the agent itself does not bloom. Therefore, it has an advantage that a good coefficient of friction is maintained for a long time from the early period of use and the effectiveness of preventing defective paper carrying can be further improved.

Examples of a peroxide crosslinking agent include one or more of those such as benzoyl peroxide, 1,1-Bis (tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(benzoylperoxy) hexane, di(tert-butylperoxy) diisopropylbenzene, 1,4-bis [(tert-butyl)peroxyisopropyl]benzene, di(tert-butylperoxy)benzoate, tert-butyl peroxybenzoate, dicumyl peroxide, tert butyl cumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di-tert-butyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy) -3-hexyne.

The blending ratio of a peroxide crosslinking agent is preferably equal to or more than 0.8 parts by mass to 100 parts by mass of the total rubber content, especially equal to or more than 1.5 parts by mass, and is preferably equal to or less than 5 parts by mass, especially equal to or less than 3.5 parts by mass. When the blending ratio of a peroxide crosslinking agent is lower than the above-described range, abrasion resistance of a paper feed roller may be decreased. Also, when the ratio is higher than the above-described range, a paper feed roller may become too hard and a desirable coefficient of friction may be less likely to be realized.

Also, a reinforcing agent or filler such as carbon black or various kinds of additives such as oil and a plasticizer may be appropriately selected for blending to a rubber composition.

A roller body 2 can be formed, for example, by a press forming method or extrusion method (a roller body forming process) using a rubber composition which is prepared as having each of the above-described components (a rubber composition preparation process). In a press forming method, for example, a roller body 2 is formed by preparing a mold having a mold cavity corresponding to the three-dimensional shape of the roller body 2 having a plurality of protruding lines 21 and recessed grooves 22 with predetermined shapes, which will be described later, on a peripheral surface 5 of the roller body 2, filling a rubber composition into the mold cavity of the mold, and then heating under pressure so that the rubber composition is crosslinked (a press molding process).

Also, in an extrusion method, a roller body 2 can be formed by extruding a rubber composition into a cylindrical shape using an extrusion machine to which a die corresponding to a sectional shape of the roller body 2 having a plurality of protruding lines 21 and recessed grooves 22 with predetermined shapes on a peripheral surface 5 of the roller body 2 is connected and then crosslinking the rubber composition (an extrusion molding process). The roller body 2 and a shaft 4 are integrated, for example, by forming an outside diameter of the shaft 4 which is larger than an inside diameter of a through hole 3 of the roller body 2 and press-fitting the shaft 4 into the through hole, by bonding the both with an adhesive, or by bonding them through vulcanization with a vulcanization adhesive when the roller body 2 is being crosslinked.

Also, at any point before and after integration of a roller body 2 and a shaft 4, the ends of the roller body 2 may be cut as necessary so that a length of the roller body 2 in the direction of the axis X, namely a width of a paper feed roller 1, becomes a predetermined value. Thus the paper feed roller 1 shown in FIG. 1 is manufactured. It should be noted that a roller body 2 may be formed with two-layer structure having an outer layer on the side of the peripheral surface and an inner surface on the side of the shaft 4. In that case, at least the outer layer needs to be formed of the above-described rubber composition.

The paper feed roller 1 of the embodiment includes, as described above, a plurality of protruding lines 21 and recessed grooves 22 which extend inclinedly relative to the direction of the axis X of the roller body 2 and has a knurled shape in which convex portions CV and concave portions CC are alternatively formed in the circumferential direction of the roller body 2. When the protruding lines 21 and the recessed grooves 22 are formed, paper to be fed comes into contact with the peripheral surface 5 of the roller body 2 by the protruding lines 21 and paper powder generated from the paper is taken by the recessed grooves 22 therein. The paper powder taken in the recessed groove 22 are removed along with rotation of the roller body 2, preventing defective paper carrying.

Also, in the embodiment, as shown in FIGS. 3 to 5, a plurality of the protruding lines 21 include one-end side protruding line portions 21 a extending from a central part of the roller body 2 in the direction of the axis X of the roller body 2 toward one end 2 a of the roller body 2 and other-end side protruding line portions 21 b extending from the central part in the direction of the axis X of the roller body 2 toward the other end 2 b of the roller body 2. As shown in FIGS. 3 to 5, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b are inclined relative to the axis X of the roller body 2 in opposite directions each other. More specifically, the one-end side protruding line portion 21 a is, when seen from the one end 2 a of the roller body 2, in a shape of right-hand helix from the one end 2 a toward the central part. On the other hand, the other-end side protruding line portion 2 b extends, when seen from the one end 2 a side of the roller body 2, in a shape of left-hand helix from the central part toward the other end 2 b. In the embodiment, the one-end side protruding line portion 21 a and the other-end side protruding line portion 21 b are, as shown in FIGS. 3 to 5, generally formed in a substantially V shape. It should be noted that the one-end side protruding line portion 21 a and the other-end side protruding line portion 21 b may be connected, as shown in FIG. 3, and may be separated, as shown in FIGS. 4 and 5, at the central part of the roller body 2.

With the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b being inclined in opposite directions each other, the roller body 2 can reduce noise caused by the shape of the paper feed roller 1 while maintaining a predetermined friction coefficient. Following is the description in detail. When protruding lines and concave portions which form convex portions and concave portions are, as in conventional configuration, provided parallel to an axis of a roller body, the rotating roller body alternately repeats being in an adhered state in which the roller body adheres to paper at the portions of the protruding lines from one end to the other end of the roller body and a separated state in which the roller body is separated from the paper at the portions of the concave portions from one end to the other end of the roller body. On the other hand, in the embodiment, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b are inclined relative to the axis X of the roller body 2. Thus, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b do not adhere to paper entirely in the direction of the axis X from the one end 2 a to the other end 2 b of the roller body 2. Therefore, the roller body 2 does not repeat being in the adhered state and the separated state entirely in the direction of the axis X from the one end 2 a to the other end 2 b of the roller body 2. Thus, abnormal noise occurring between the peripheral surface 5 of the roller body 2 and paper can be reduced when the roller body 2 rotates.

In the embodiment, as shown in FIGS. 3 to 5, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b extend at substantially equal angles relative to the axis X of the roller body 2. When the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b extend at substantially equal angles relative to the axis X, the paper passing the roller body 2 is stably carried in the direction perpendicular to the axis X. The angles between each of the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b and the axis X of the roller body 2 (the angle θ in FIG. 3) are not particularly limited. However, the angles of extending directions of the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b relative to the axis X of the roller body 2 can be, for example, no less than 3° and no more than 40°. When the angles of extending directions of the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b relative to the axis X of the roller body 2 are no less than 3° and no more than 40° (3°≦θ≦40°), effect of reducing the abnormal noise is obtained from protruding lines 21 being inclined at a predetermined angle, and at the same time, load on paper is restrained by restricting the angle within a predetermined range. Thus, the abnormal noise is reduced, and also wrinkles occurring due to the load on paper are prevented. Also, it is more preferable that the angles of the extending directions of the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b relative to the axis X of the roller body 2 are no less than 5° and no more than 30 (5°≦θ≦30°). In this case, the effect of reducing the abnormal noise is increased and wrinkles can be further prevented from occurring. Also, it is even more preferable that the angles of the extending directions of the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b relative to the axis X of the roller body 2 are no less than 5° and no more than 15° (5°≦θ≦15°). In this case, the effect of reducing the abnormal noise is further increased and wrinkles can be even further prevented from occurring. Also, by making the angle of the protruding lines 21 relative to the axis X as small as no more than 15°, defects are less likely to occur to the roller body 2 at the time of molding the roller body 2 and rubber chipping or the like of the roller body 2 while being used can be inhibited. More specifically, for example, when molding of the roller body 2 is performed by transfer press molding, the molded roller body 2 is moved from a mold in the direction of the axis X to be demolded. In this case, by making the angle of the protruding lines 21 as small as no more than 15°, resistance applied to the protruding lines 21 of the roller body 2 upon demolding of the roller body 2 from the mold can be reduced. Therefore, rubber chipping during molding process such as demolding of the roller body 2 and rubber chipping while in use resulted from the resistance applied during the molding can be inhibited.

Also, as shown in FIG. 4, one-end side recessed grooves 22 a and other-end side recessed grooves 22 b can be separated at the central part in the direction of the axis X of the roller body 2. Specifically, the roller body 2 includes, at the central part of the roller body 2, an annular part 23 (having a circular cross section) which has a width in the direction of the axis X and does not have concave and convex shapes in the circumferential direction, wherein the ends at the central part of the one-end side recessed grooves 22 a and the other-end side recessed grooves 22 b are discontinued on the both sides of the annular part 23 in the direction of the axis X.

Also, in an embodiment shown in FIG. 5, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b of the roller body 2 are provided so that ends Ea of the one-end side protruding line portions 21 a at the central part of the roller body 2 and ends Eb of the other-end side protruding line portions 21 b at the central part of the roller body 2 are offset in the circumferential direction of the roller body 2. In this case, the protruding lines 21 and the recessed grooves 22 have a phase difference between the side of one end 2 a of the roller body 2 (the left hand side of the roller body 2 in FIG. 5) and the side of the other end 2 b (the right hand side of the roller body 2 in FIG. 5). In other words, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b (and the one-end side recessed grooves 22 a and the other-end side recessed grooves 22 b) of the roller body 2 are not provided so as to be symmetrical relative to the central part when seen in a side view of the roller body 2, but formed so as to be offset in the circumferential direction. More specifically, the ends Ea of the one-end side protruding line portions 21 a at the central part and the ends Eb of the other-end side protruding line portions 21 b at the central part are offset in the circumferential direction of the roller body 2, and the protruding lines 21 and the recessed grooves 22 have a phase difference between the side of one end and the side of the other end. Also, in this case, second ends Ea2 of the one-end side protruding line portions 21 a located on the side of the one end 2 a of the roller body 2 and second ends Eb2 of the other-end side protruding line portions 2 1 b located on the side of the other end 2 b of the roller body 2 are offset in the circumference direction of the roller body 2, and the protruding lines 21 and the recessed grooves 22 have a phase difference between the side of one end and the side of the other end. When the protruding lines 21 and the recessed grooves 22 are inclined relative to the axis X (as shown in FIG. 3, for example), influence on the abnormal noise caused by adhering and separating between the roller body 2 and paper are larger at the central part and the both ends (the one end 2 a and the other end 2 b) of the roller body 2. As described above, when the ends Ea of the one-end side protruding line portions 21 a at the central part and the ends Eb of the other-end side protruding line portions 21 b at the central part are provided so as to be offset in the circumferential direction of the roller body 2, timings of adhering and timings of separating disperse between the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b at the central part as well as at the both ends (the one end 2 a and the other end 2 b) of the roller body 2. Thus, the one-end side protruding line portions 21 a and the other-end side protruding line portions 21 b do not simultaneously adhere to nor separate from paper at the central part and the both ends of the roller body 2, and the abnormal noise can be further reduced.

It should be noted that, for the roller body 2 shown in FIG. 5, the entire roller body 2 may be integrally molded with a mold, or an one-end side roller member (a member constituting the left half in FIG. 5) and an other-end side roller member (a member constituting the right half in FIG. 5) of the roller body 2 may be manufactured separately and the two roller members may be combined into the roller body 2.

Shapes of the convex portions CV and the concave portions CC are not particularly limited. In the embodiment, as shown in FIG. 2, the convex portion CV is connected, by curvature portion CP having a curvature radius R1, to side wall S forming the concave portion CC formed on the both sides of the convex portion CV in the circumferential direction. More specifically, the convex portion CV has substantially flat top face T along the peripheral surface 5 of the roller body 2, the top face T forming the convex portion CV and the side wall S of the concave portion CC are connected by the curvature portion CP having the curvature radius R1. In the concave portion CC, a pair of side walls S are connected by a base B having a curvature radius R2. The curvature radius R1 of the curvature portion CP and the curvature radius R2 of the base B of the concave portion CC are not particularly limited. In the embodiment, the roller body 2 is formed so that the curvature radius R2 of the base B is the similar curvature radius to the curvature radius R1 of the curvature portion CP. A height H from the base B to the top face T of the concave portion CC is not particularly limited as long as it has a predetermined height which allows paper powder to be taken therein.

The substantially flat top face T constituting the convex portion CV has a predetermined width W1. The concave portion CC formed between a pair of the convex portions CV has a predetermined width W2. Dimension of the width W1 of the top face T and dimension of the width W2 of the concave portion CC are not particularly limited. For example, it is preferable that the width W1 of the top face T is larger than the width W2 of the concave portion CC (W1≧W2). In this case, contact area of the rubber and paper is larger than a certain area. Therefore, the load applied to the rubber is within a predetermined range and abrasion of the rubber can be suppressed.

In the embodiment, the radius of the roller body 2 is designed to be 10.62 mm and the angle from the base B of one concave portion CC to the next base B of the other concave portion CC in the circumferential direction is designed to be 9°. However, dimension and angle of each part of the roller body 2 are not particularly limited.

In the following, examples and a comparative example of the present invention are explained. However, the present invention is not limited to the examples only.

EXAMPLE

First, manufacturing method and testing method of paper feed roller of the examples and comparative example will be explained.

Manufacturing Method

A transfer mold having concave and convex shapes corresponding to a roller body 2 in which the concave and convex shapes shown in FIG. 2 are formed in the circumferential direction thereof and the protruding lines 21 and the recessed grooves 22 are inclined as shown in FIG. 3 was prepared. A paper feed roller of Example 1 was made, with this transfer mold, by vulcanizing molding a rubber composition comprising silicone rubber, molding it into a cylindrical shape, and fitting the molded sample cut in a predetermined width (25 mm) into a resin core for paper feeding. Also, a transfer mold having concave and convex shapes corresponding to a roller body 2 having a phase difference in which the concave and convex shapes shown in FIG. 2 are formed in the circumferential direction and the protruding lines 21 and the recessed grooves 22 are inclined as shown in FIG. 5 was prepared. A paper feed roller of Example 2 was made, with this transfer mold, by fitting the molded sample molded in the same way as Example 1 into a resin core for paper feeding. Also, a transfer mold having concave and convex shapes corresponding to a roller body in which the concave and convex shapes shown in FIG. 2 are formed in the circumferential direction and the protruding lines and the recessed grooves extend in parallel with the axial direction of the roller body was prepared. A paper feed roller of Comparative Example 1 was made, with this transfer mold, by fitting the molded sample molded in the same way as Example 1 and 2 into a resin core for paper feeding. It should be noted that degrees of rubber hardness were 30° in Examples 1, 2 and Comparative Example 1, respectively.

Sound Collecting Test

The paper feed rollers of Example 1, 2, and Comparative Example 1 were set to a device capable of successive paper passing and rotated at the rotational speed of 600 mm/s with the load of 400 gf applied on them. Volumes of sound in each time were collected using an integral type noise meter. Measurement was performed, to pick up as little sound of a motor of the device as possible, at the lateral side of the roller opposite to the motor. Results of the sound collecting were shown as noise value (dB) in Table 1. It should be noted that the noise values in Table 1 include operating sound of the motor, which was 30.3 db; therefore, the actual noise value of the paper feed rollers themselves are smaller values than the noise value shown in Table 1.

TABLE 1 Noise performance Noise value (dB) Evaluation Example 1 63.5 ◯ Example 2 62.4 ⊚ Comparative Example 76.1 X

As shown in Table 1, the noise values of Example 1 and Example 2 were smaller than Comparative Example 1 in which the protruding lines and the recessed grooves are formed in parallel with the axis of the roller body. Therefore, it was found that when protruding lines and recessed grooves are provided so as to be inclined relative to an axis of a roller body, abnormal noise which occurs as paper passes through the roller body becomes less loud. Also, reduction of the abnormal noise is more effective in Example 2 in which the protruding lines have a phase difference than Example 1 which has no phase difference. Therefore, it was found that when protruding lines have a phase difference, the abnormal noise can be further reduced.

REFERENCE SIGNS

1 paper feed roller 2 roller body 21 protruding line 21 a one-end side protruding line portion 21 b other-end side protruding line portion 22 recessed groove 22 a one-end side recessed groove 22 b other-end side recessed groove 23 annular part 2 a one end of roller body 2 b other end of roller body 3 through hole 4 shaft 5 peripheral surface of roller body B base CC concave portion CP curvature portion CV convex portion Ea end of one-end side protruding line portion at central part Eb end of other-end side protruding line portion at central part S side wall T top face 

What is claimed is:
 1. A paper feed roller comprising a roller body formed of elastic material in a cylindrical shape, wherein the roller body includes a plurality of protruding lines and recessed grooves inclinedly extending relative to an axis of the roller body so that convex portions with predetermined width and concave portions with predetermined width are alternatively formed in a circumferential direction of a peripheral surface of the roller body, and the plurality of protruding lines include one-end side protruding line portions extending from a central part of the roller body in a direction of an axis of the roller body toward one end of the roller body and other-end side protruding line portions extending from the central part in the direction of the axis of the roller body toward an other end of the roller body, and the one-end side protruding line portions and the other-end side protruding line portions are inclined relative to the axis of the roller body in opposite directions each other.
 2. The paper feed roller according to claim 1, wherein the one-end side protruding line portions and the other-end side protruding line portions extend at substantially equal angles relative to the axis of the roller body and the angles of extending directions of the one-end side protruding line portions and the other-end side protruding line portions relative to the axis of the roller body are no less than 5° and no more than 15°.
 3. The paper feed roller according to claim 1, wherein the one-end side protruding line portions and the other-end side protruding line portions are provided so that ends of the one-end side protruding line portions at the central part of the roller body and ends of the other-end side protruding line portions at the central part of the roller body are offset in the circumferential direction of the roller body.
 4. Image forming apparatus comprising the paper feeding roller according to claim
 1. 